The objective of this study is to determine whether direct aspiration of enlarge parathyroid glands under CT or ultrasound control can replace selective venous sampling and PTH assay as a localizing techniques. Selective venous sampling is tedious, time-consuming, and involves significant radiation to both patient and angiographer. An elevation of parathyroid hormone in a selective vein localizes the general site of the adenoma but does not pinpoint it for easy surgical excision. An incrasing number of paraghyroid adenomas have been identified in the neck and uppor portions of the mediastinum both at CT scanning and ultrasound. In spite of bolus injections, distinguishing these soft tissue densities from vascular or thymic structures remains a problem. Under either CT or ultrasonographic control, a skinny needle can generally be introduced into these glands and minute amounts of tissue juices aspirated